Start ups need people who know what they are doing. These people make well above the median. Making market salary in an expensive area like the Bay Area is not negotiable, and it's certainly not traded for equity.

The equity is what gets talent to accept the tremendous risk of leaving a solid position with an established company, for an unstable one at a high risk venture.

If you can't afford to pay market rate, that means you're not funded enough to be hiring. Equity is in addition to market salary.